1. Field of the Invention
The present invention relates generally to backpack and carrier assemblies.
2. Description of Prior Art
During normal walking and running, the shoulders and pelvis rotate in opposite directions. This relative counter-rotation results as each side of the pelvis follows its associated leg as that leg extends forward to begin a step. While that leg remains in place on the ground, it serves as a pivot about which the pelvis rotates as it carries the other leg and torso forward. The upper torso, in turn, remains oriented generally in the direction of forward movement; thus, there is a resulting opposing relative movement of pelvis to upper torso.
Relative to the torso, the pelvic movements are complex partial rotations in several planes, alternatively clockwise and counter-clockwise. The torso also operates as the counter balancing inertial mass against which connecting muscles pull in order to generate pelvic rotation, leg movement and thrust. The effectiveness of the torso as a counter-balancing mass is enhanced by coordinated swinging of the arms, choreographed so as to oppose pelvic rotation. Torso mass is further increased, and its effects amplified, by the additional mass of a loaded backpack carried by the shoulders and upper torso. The additional mass of a backpack load allows torso counter-movement to be shorter and still provide the appropriate counter-force to hip rotation.
Given the downward pull of gravity, backpack weight must be borne by generally upward-facing horizontal body surfaces. The shoulders are most commonly used for this purpose; thus, most backpacks have shoulder straps. An alternative or supplementary method is to transfer all or some of the load to a belt worn about the user's pelvic area. Weight thus transferred by the frame to the belt is passed on to the lower body through the hydraulic action of the belt in squeezing the pelvic area. Therefore, this soft area of the body is in effect squeezed into a relatively firm vertical column, the outer skin of which is gripped by the belt through friction. Inside this vertical column (which is composed of muscles, veins, arteries and internal organs), weight is transferred to the pelvis. Some weight also reaches the pelvis just below the skin surface which is not covered by muscles. Such squeezing has the unfortunate effect of interfering with both muscular flexion and blood flow to and from the legs and throughout the pelvic area.
In addition to the above-mentioned problems which belt squeeze causes in various soft tissues, most versions of the belt-and-frame backpack also tend to restrict pelvic rotation. While one can walk without rotating the pelvis, this type of movement is both awkward and tiring; each step is significantly shortened. In such a situation, the pelvis not only does not contribute its own additional extension to step length, but also the hip joint reaches its angular rotational limit early in the stride, as do the relative tendons, because of limited pelvic rotation about the associated transverse axis.
Even in a beltless backpack borne only by the shoulders, the relative counter-rotational movement discussed above during natural walking is hindered. Because the backpack is attached to and moves with the shoulders, its lower front-facing portion moves in a direction opposite to that of the lower rear-facing portion of the user's back. Given the "overhung" mechanics of a shoulder-supported backpack, the lower part of the backpack can press with considerable forward force against the lumbar region of the user. The result is that the combination of this friction with the opposing lateral directions of motion hinders the free rotational movement of the pelvis, and also causes jiggling of the backpack.
So-called "fanny" packs are particularly problematic. Such packs cause the user to suffer from the above-described squeeze problems by transferring all of the weight to a hip belt. But there is an additional problem with such packs caused by adding mass to the pelvic area. Given the relationship of mass to inertia and motion, the effectiveness of upper torso mass as an inertial stabilizer and counterbalance is reduced relative to the increased mass associated with the pelvis in such a "fanny" pack. Worse, the rotating pelvis must now propel the entire mass of the loaded pack, not only forward with the body as a whole, but also along the pelvis' own complicated path, which comprises alternating clockwise and counter-clockwise rotations and other movements in three dimensions.
Specific prior art backpack arrangements of interest are disclosed in the following U.S. Pat. Nos.: 3,033,431 to Henderson et al.; 3,114,486 to Flexman; 3,191,828 to Senne; 3,206,087 to Tyrrell; 3,254,816 to Gray; 3,282,483 to Babcock; 3,355,075 to Dean; 3,516,586 to Farnbach; 3,653,566 to Owens; 3,733,017 to Pletz; 3,831,827 to Olson; 3,889,859 to Joseph; 3,938,718 to Madison; 4,013,201 to Potter; 4,015,759 to Dreissigacker et al.; 4,099,657 to Zufich; 4,189,076 to Zufich; 4,194,656 to Zufich; 4,214,685 to Pletz; 4,303,186 to Ollinger; 4,369,903 to Wilkes; 4,479,595 to Opsal; and 4,504,002 to Hall.